1. The Nature of Host Defenses

2. There are at Least Three Lines of Defense Against Microbial Invasion

3. 1st line of defense – Non-Specific Barriers
intact skin
mucous membranes & their secretions
2nd line of defense - Non-Specific
phagocytic white blood cells
inflammation -complement
fever -interferon
3rd line of defense- Specific
B & T lymphocytes
antibodies
nonspecific

4. Physical or Anatomical Barriers
Cornefication of outermost layer of skin
Flushing effect of sweat glands
Rapid replacement of damaged cells
Mucous impedes attachment & entry of bacteria
Blinking & tear production
Nasal hair traps larger particles

5. Chemical Defenses Sebaceous secretions Lysozyme in tears
High lactic acid & electrolyte concentration in sweat
Skin’s acidic pH
Hydrochloric acid in stomach
Digestive juices and bile of intestines
Semen contains antimicrobial agents
Vagina has acidic pH

6. Genetic Defenses Some pathogens have great specificity
Some genetic differences exist in susceptibility

7. A Healthy Immune System is Responsible for
Surveillance of the body
Recognition of foreign material
Destruction of entities deemed to be foreign

8. Immune System Definitions
White blood cells (leukocytes) – have an innate ability to recognize and distinguish foreign material
Non-self – foreign material
Self – normal cells of the body
Pathogen-associated patterns (PAMPs) – molecules shared by microorganisms
Pathogen recognition receptors (PRRs) – receptors on WBCs for PAMPs

10. The Immune System
A large, complex, and diffuse network of cells and fluids that penetrate into every organ and tissue
The four major subdivisions of immune system:
Reticuloendothelial system (RES)
Extracellular fluid (ECF)
Bloodstream
Lymphatic system

11. Reticuloendothelial System (RES)
Network of connective tissue fibers that interconnects other cells and meshes with the connective tissue network surrounding organs
Inhabited by phagocytic cells – mononuclear phagocyte system – macrophages ready to attack and ingest microbes that passed the first line of defense

13. White Blood Cells (Leukocytes) are the Body’s Immune Cells

14. Leukocytes
Neutrophils % - lobed nuclei with lavender granules; phagocytes
Eosinophils – 1-3% - orange granules & bilobed nucleus; destroy eucaryotic pathogens
Basophils, mast cells – 0.5%; constricted nuclei, dark blue granules; release chemical mediators

15. Leukocytes - Continued
Lymphocytes – 20-35% - large nucleus; B & T cells involved in the specific immune response
Monocytes, macrophages – 3-7%- large nucleus; phagocytic

17. Lymphatic System
Provides an auxiliary route for return of extracellular fluid to the circulatory system
Acts as a drain-off system for the inflammatory response
Renders surveillance, recognition, and protection against foreign material

18. Lymphatic Vessels
Lymphatic capillaries permeate all parts of the body except the CNS
Thin walls easily permeated by extracellular fluid which is then moved by contraction of skeletal muscles
Functions to return lymph to circulation; flow is one-direction-toward the heart-eventually returning to blood stream

20. Lymphatic Fluid
Lymph is a plasmalike liquid carried by lymphatic circulation
Formed when blood components move out of blood vessels into extracellular spaces
Made up of water, dissolved salts, 2-5% proteins
Transports white blood cells, fats, cellular debris & infectious agents

21. Lymph Nodes
Small, encapsulated, bean-shaped organs stationed along lymphatic channels & large blood vessels of the thoracic and abdominal cavities
Contain populations of T and B lymphocytes in sinuses
Act as sites for encounters with microbes leading to specific immune responses

23. Actions of the Second Line of Defense
Recognition
Inflammation
Phagocytosis
Interferon
Complement

24. Recognition
Protein receptors within cell membrane of macrophages, called Toll-like receptors
Detect foreign molecules and signal the macrophage to produce chemicals which:
stimulate an inflammatory response (nonspecific)
promote the activity of B and T cells (specific)

26. Inflammation – a Generalized Response to Tissue Injury

27. Stages of Inflammation
Blood vessels constrict, then dilate in response to chemical mediators and cytokines
Edema swells tissues, helping prevent spread of infection
WBC’s, microbes, debris and fluid collect to form pus
Pyrogens (endogenous or exogenous) may induce fever
Macrophages and neutrophils engage in phagocytosis

29. Activities of Phagocytes
To survey tissue compartments & discover microbes, particulate matter & dead or injured cells
To invade and eliminate these materials
To extract immunogenic information from foreign matter

30. Characteristics of Leukocytes
Diapedesis – migration of cells out of blood vessels into the tissues
Chemotaxis – migration in response to specific chemicals at the site of injury or infection

32. Phagocytosis

33. Fever: Another Non-Specific Response
Elevated body temperature in response to a chemical mediator
Inhibits temperature-sensitive microorganisms
Impedes bacterial nutrition
Stimulates immune reactions

34. Interferon Small proteins produced by specific cells
Alpha interferon- lymphocytes & macrophages
Beta interferon – fibroblasts & epithelial cells
Gamma interferon – T cells
Produced in response to viruses, RNA, immune products, and various antigens
Bind to cell surfaces and induce expression of antiviral proteins
Inhibit expression of cancer genes

36. Complement
Consists of 26 blood proteins that work in concert to destroy bacteria, fungi and enveloped viruses
Complement proteins are activated by cleavage
Classical pathway
Alternative pathway

37. Complement Pathways
Classical pathway – activated by the presence of antibody bound to microorganism
Alternative pathway – begins when complement proteins bind to normal cell wall and surface components of microorganisms

38. Complement Uses a Cascade System
One component activates another which activates another, and so on

40. Complement